Keyboard systems that detect the position of each of a plural keys are known. When a key is pressed in the keyboard systems, the sound production information is transmitted to a sound source. In these keyboards, when a key release is detected, sound production is stopped. In addition, the keyboard systems that continuously detect key speed when a key is pressed are known. The velocity is calculated in the keyboard systems when the key stroke reaches the prescribed depth, based on the fastest key stroke out of all the key stroke speeds. Once the velocity is calculated, the sound output begins to be produced. The sound source generates a sound when the depth of the key reaches a predetermined depth.